As already mentioned, the latest outbreak of cholera began in Peru in 1991 and spread quickly to nearly all neighboring countries(84). The disease evolved in explosive epidemics, the largestrecorded since the beginning of the seventh pandemic in Sulawesi(the Celebes), Indonesia, in 1961. The epidemics behaved differentlyin the nations of Latin America affected by cholera, accordingto prevailing levels of poverty, health education, sanitation,and risk factors (84).

In Peru, cholera appeared in January 1991, and at the end of the summer, Chancay, Chimbote, Piura, Lima, Trujello, and otherlocalities were affected in succession or simultaneously along1200 km of the Pacific Coast (85). In 3 weeks, the epidemiccovered >2000 km of coastal areas and caused 30,000 cases and114 deaths in the first 7 days.

Cholera reached Ecuador 6 weeks after the outbreak in Peru, and spread throughout the country within 2 months; however, theintensity of the epidemic was less than in Peru. A milder outbreakfollowed in Columbia. The epidemic in Brazil appeared at the borderof Columbia and Peru, in the Amazon, São Paolo, and Rio de Janeirobasins, in July to September. Eight months later, the diseasereached Bolivia.

All South American countries were affected in 1991 except Argentina and Paraguay, the latter having some cases in 1992. Uruguaywas fortunate in being relatively free of cholera cases. Mexicowas hit on 13 June 1991; subsequently outbreaks occurred in Guatemalain July, in El Salvador in August, and then in Honduras. Nicaraguareported cholera early in 1992, and even worse epidemics occurredin 1993. Chile had its first case confirmed on 12 April 1991 inSantiago, 1700 km south of Peru. By 1992, there were 99 cases.In Costa Rica, the first case appeared on 5 January 1991. Morethan 1.5% of the Peruvian population was estimated to have comedown with cholera during the first 3 months of 1991. The sixthpandemic, seventh pandemic, and U.S. Gulf Coast isolates wereconcluded to be three clones, apparently evolving independentlyfrom environmental, nontoxigenic, non-01 El Tor organisms (70).The 0139 isolates are concluded to have evolved from seventh pandemicisolates of V. cholerae 01 El Tor.

El Niño Events

The trade winds blowing westward across the central Pacific force warm surface water from the seas near Peru toward Tahiti.Thus, cold currents, rich in nutrients and phytoplankton, circulateup from the ocean bottom off the Peruvian coast to replace thewarm water moving west. El Niño is a warming of surface watersin the Central Pacific of 1°C greater than normal.

Coincidental to the cholera outbreak in Peru was a warm event related to El Niño in the tropical Pacific from 1990 to June1995 and is the longest on record since 1882. It occurred in thecontext of a tendency for more frequent El Niño events and fewerLa Niña events since the late 1970s (86). Returning every 4years on average and usually lasting approximately a year, ElNiño, an unusual warming in the central Pacific Ocean, createsstorms and disrupts wind patterns (87). The surprise during1991 to 1995 was that the El Niño lasted for more than 3 years,the longest time period since monitoring began in the 1870s.

Recent interannual changes in the strength and seasonal evolution of the surface level southwest monsoon winds have been relatedto variations in summer phytoplankton blooms of the northwesternArabian Sea and also the Bay of Bengal. In the Bay of Bengal,synthesis of satellite remote sensing with analysis of in situhydrographic and meteorological data sets, and cholera case datafor Bangladesh, has provided evidence that cholera cases occurfollowing a rise in ocean surface temperatures (88) (Fig. 1).

From 1979 to 1981, monsoon phytoplankton blooms in the northwest Arabian sea peaked during August and September, and appearedto lag the development of open-sea upwelling by at least 1 month.Coastal upwelling, from May to September, yielded the most extremeconcentrations of phytoplankton biomass. Phytoplankton biomasson the Omani continental shelf increased during both the earlyand late phases of the 1980 southwest monsoon, because of strongercoastal upwelling. The Somali current in the Arabian Sea has muchthe same directional flow as currents in the Bay of Bengal (89).

Kiorboe and Neilsen (42) studied seasonal distributions of biomass, egg production, and production rates of pelagic copepodcommunities. Copepod production was found to be episodic and occurringin bursts associated with phytoplankton blooms. The seasonal distributionof copepod biomass was unimodal; concentrations peaked in Juneand July in Denmark, where the studies were done. A spring productionburst was observed, and egg production rates varied significantlywith concentrations of chlorophyll and total microplankton biomass,but only weakly with the abundance of dinoflagellates, nanoflagellates,ciliates, and copepod nauplii. Significant copepod egg productionoccurred only when concentrations of diatoms and other large phytoplankterswere high. The conclusion is that copepod production depends onepisodic phytoplankton blooms.

From all of this evidence, it is now possible to utilize remote sensing and computer processing to integrate ecological, epidemiological,and remotely sensed spatial data for the purpose of developingpredictive models of cholera outbreaks (40). The ability topredict conditions conducive to pandemics of cholera should allowpublic health measures to be taken prospectively, rather thanretrospectively.

In this case study of cholera, the interdisciplinary cross-cut of oceanography, ecology, microbiology, marine biology, epidemiology,medicine, and satellite imagery (space science) will allow a newconceptualization and understanding of this historic scourge ofhumankind and, ultimately, prevention of global pandemics of thisdisease.